Apparatus for applying strips of resistive material

ABSTRACT

A heated window carrying a plurality of spaced parallel connected electrical resistance bands of different lengths, each of the resistance bands being made to have substantially the same heating effect per unit area by making them of different cross sections or of different linear resistivity. The resistance bands may be made by a novel method including depositing pasty compositions in lines upon the glass, such compositions including a suspension of powdered metal and a low fusion point frit. The linear resistivity of the bands may be varied by changing the proportion of metal to frit in the composition. The novel apparatus for depositing the bands upon the glass includes toothed rollers travelling in non-slipping relationship in contact with the glass, the roller transferring the composition from a feeding means to the glass as it revolves.

I Unlted States Patent 11 1 1111 3,874,330 Zoccolini 1 Apr. 1, 1975 [54] APPARATUS FOR APPLYING STRIPS ()F 2,762,072 9/1956 Madalinski 40l/208 RESISTIVE MATERIAL 2,788,538 4/l957 Benkowski... 401/208 2,855,892 10/1958 Lea eta] 118/241 x 1 Inventor: Gino Zoecolim, Milan. Italy 3,185,130 5/1965 Pratt; 118/241 x [73] Assignee: Saint-Gobian Industries, Neuilly sur I i i i l i I i i i 3 Seine France [22] Filed: Feb. 8, 1972 Primary Examiner-John P. McIntosh [2!] App]. NO: 224,557 Attorney, Agent, or Firm-Pennie & Edmonds Related U.S- Application Data [63] lCgninuation-m-part of Ser. No. 860,375, Sept. 24, A heated Window y g a plurality of Spaced paral lel connected electrical resistance bands of different [30] Foreign Application Priority Data lengths, each of the reslstance bands bemg made to s 77 1968 F 68167881 have substantlally the same heating effect per un1t rmce area by making them of different cross sections or of different linear resistivity. The resistance bands may [52] U.S. Cl 118/207, 33/41 C, l4l08l//2220l8, be made by a novel method i l di d ositing pasty $1 I t Cl B05 U02 compositions in lines upon the glass, such composig 'l 241 tions including a suspension of powdered metal and a l g ;6 b low fusion point frit. The linear resistivity of the bands 36 37 4 may be varied by changing the proportion of metal to frit in the composition. The novel apparatus for depositing the bands upon the glass includes toothed rollers [56] References cued travelling in non-slipping relationship in contact with UNITED STATES PATENTS the glass, the roller transferring the composition from 1,965,753 7/1934 Scoles 401/193 X a feeding means to the glass as it revolves. 2,494,160 1/1950 Bihary .1 118/211 x 2.582.861 1/1952 Coombs 401 208 1 Clalm, 9 Drawlng Figures PATENTEI] APR 1 I975 SHEET 1 (IF 3 VITREOUS GLAZE CONTENT BY WEIGHT m QU B Y G v 5 4 3N.2 -1 1; 223% $2: :2: NE 32 2:5

PATENTED APR 1 SHEET 2 BF 3 PATENTEU 1 9 5 sum 3 Inf 3 APPARATUS FOR APPLYING STRIPS OF RESISTIVE MATERIAL This application is a continuation in part of my application Ser. No. 860,575 filed Sept. 24, 1969.

The present invention relates to the making of heated windows for vehicles. Such windows may be simple tempered safety glass provided on at least one of its faces with electrically conducting bands forming resistance heaters disposed on the glass with spaces between them. The ends of such bands, which are disposed parallel to each other, are connected to convenient terminal bands or good electrical conductivity.

The said bands are made up of an electrically conducting composition have a predetermined resistivity, such composition having preferably been made by baking or firing a suspension of fine metal such as powdered silver and a frit having a low fusion point in an organic vehicle. The deposition of such suspension in the form of bands on at least one of the faces of the glass may be effected by the extrusion of such suspension in the form of thin filaments by the means of nozzles which move at a uniform speed in a predetermined path along the surface of the glass; as an alternative such bands may be laid down by the silk-screen pro cess.

In the silk-screen process the resistance lines are applied by spreading the fluid paste over the lines in the screen with a doctor blade, a process which does not readily admit of the application of bands of different composition in industrial practice. It is an object of this invention to apply bands of different composition or of different width, or both, simultaneously. To accomplish this a plurality of reservoirs containing the same or different compositions are mounted in gang, each supplying a chosen composition to a roller of selected width mounted parallel to rollers supplied by the others. By guiding the gang along a selected path any desired pattern of parallel lines can be applied.

This invention has another advantage that when it is desirable to reduce the resistance of an applied line the present apparatus and method permits it to be accomplished without difficulty, the apparatus being guided over the original lines to apply a coat which increases the cross section and reduces the resistance. It also permits the addition of new thickness to part ofa line only, producing different resistivities and different heating effects in parts of the same line, a very useful device for insuring maximum heating in the most essential area of a windshield, the area which must be kept clear at all times despite conditions of weather and temperature.

It has also been proposed to reinforce such bands locally by a further deposit of metal such copper by electroplating, and finally to protect the metallic bands by coatings of enamel or varnish.

In general the resistance bands, disposed parallel to each other, are connected to the terminal or collective bands in such manner that all of the bands have equal resistances. However, because of the form of the window or the disposition of the network of bands, the resistance bands may be of different lengths; in such case even through all the bands have the same specific resistance they will have different heating effects because of their different lengths. It is obvious that an unequal heating of the various heating bands is undesirable. It is thus necessary to correct such inequality and to provide resistance bands having the same heating effect so they provide as far as possible a homogeneous field of visibility through the glass.

The present invention has as its primary object the provision of resistance bands having a uniform cross section throughout their lengths, such cross section being independent of the speed of which the bands were laid down upon the glass. To obtain such result, in accordance with the invention there is employed an apparatus which permits the application of the electrically conducting composition on the glass by relative travel between the apparatus and the glass which it contacts, such apparatus carrying a plurality of cavities which are opened to their exterior which function to feed the same composition progressively at a controlled rate from a feeding means to the surface of the glass.

Such apparatus includes essentially a rotatable means such as a small roll which travels at a convenient speed along the glass, the roll being pressed against the glass with a predetermined desired pressure. The roll is provided on its periphery with a plurality of grooves which are separated from each other by lands, the periphery of the roll being in non-slipping relationship with the glass so that the grooves travel successfully from the feeding means to the glass as the roll rotates. During such travel of the roll along the glass and its consequent rotation the grooves which are successively filled are emptied and thus lay down upon the glass aligned gobs of composition which flow together to form a band having a predetermined cross section.

In accordance with the invention it is possible to regulate the cross section of the bands which result from the spreading out of the gobs of deposited composition; as a consequence the resistivities of the bands after firing or baking may be predetermined by providing grooves and lands of the required dimensions upon the periphery of the roller. The cross sectional area of the bands thus produced is independent of the speed of travel of the roller on the glass.

The present invention allows the electrically conducting composition to be laid down upon the glass in such manner as to obtain bands whose resistance very closely approximates the desired value. It is also easy to apply all of the bands to the glass at one time by use of an apparatus including a plurality of rolls each with its individual feeding means, such apparatus compensating for the different lengths; of the respective bands so that all of the bands have the same heating effect per unit area.

The electrical resistivity of the electrically conduc tive compositions which are preferably employed in the practice of the invention, particularly of those compositions which include a suspension of finely divided metal such as silver, may be substantially increased in a predetermined manner by increasing the proportion of the vitreous glaze which is employed in the mixture, in particular by incorporating a frit having a lowfusion point in commercially available electrically conducting compositions. As a result, it is possible to regulate in a desired manner the resistance of certain conductive bands or of a group of such bands without modifying their geometry. The resistivity of the various bands may be altered as required by changing the content of the vitreous glaze which is fed to the various bands by the depositing rollers. Heating networks thus produced have a satisfactory appearance, since all of the bands are of the same cross section even though various ones of them have resistivities different from the other.

The invention retains its utility when the heating bands are reinforced by electroplating, since the amount of added reinforcing metal varies in inverse proportion to the initial resistance of the bands.

Other characteristics and advantages of the invention will appear in the following detailed description in which reference is made to drawings showing exemplary but non-limiting embodiments:

In the drawings:

FIG. 1 is a curve showing the electrical resistivity of a composition in accordance with the invention as a function of the concentration of the vitreous glaze;

FIG. 2 is a view in side elevation of a preferred form of the apparatus for the application of such composition to the glass, such apparatus being fixed on a frame which permits the band to be laid down automatically;

FIG. 3 is a view in vertical cross section taken along the line 33 of FIG. 2;

FIG. 4 is an exploded view of the apparatus of FIGS. 2 and 3, the view being partially in vertical section and partially in side elevation;

FIG. 5 is an exploded view in detail on a large scale showing the mounting of the toothed roller on the apparatus;

FIG. 6 is a view in detail on a large scale showing in section the periphery of the toothed roller as it cooperates with the surface of the glass;

FIGS. 7 and 8 are schematic views of two different forms of electrically heated rear windows of an automobile, the two windows being heated by electrical networks of different configurations; and

FIG. 9 is a schematic view of a heated window having a heating network of still different configuration, such network being provided with electrical current through a schematically illustrated control system.

As has been indicated above, the improvements provided by the present invention result largely from the possibility of regulating as desired the resistivity of each of the electrical resistance bands laid down upon the glass, primarily providing resistance bands of similar and uniform dimensions but different resistivities as the result of the incorporation in the compositions of varying proportions of the frit which forms the glaze.

Work done by the inventor has established the fact that the increase in the proportion of the glaze associated with the metal in the electrically conducting composition results in an increase in the resistivity in accordance with a substantially exponential function. This is shown, for example, in FIG. 1 in which the intrinsic resistivity of such a coating measured as the resistance of a square of fixed thickness and expressed as (2/4 l()' is plotted against the content of the vitreous glass, expressed C,,,., which is given in percent by weight of the electrically conducting composition. This method of describing the resistivity of such coating seems unusual but is actually standard practice in this art. The curve shown in FIG. I was not arrived at analytically but has been found by experiment being given in the following table:

Additional vitreous glaze Electrical resistivity -Continued Additional vitreous glaze Electrical resistivity (percent by weight) (.Q/unit area) 50% 3.7 X IO" 60% 8.7 X 10 It must be remembered that in order to obtain a satisfactory window the resistance bands ought to be of small thickness, on the order of 0.01 mm. for example, of a uniform width, generally between 0.5 and 1 mm., and by preference between about 0.7 and 0.9 mm., the borders of the bands being perfectly defined, and the bands having a resistance which is almost exactly that desired. Such bands may be easily obtained by means of the apparatus shown in FIGS. 2-6, inclusive, which forms a part of the invention, and which will now be described.

The principal part of such apparatus is formed by a small toothed roller 10, the profile ofa typical such roller being shown in detail in FIGS. 5 and 6. The thickness (axial length) of such roller is determined experimentally as a function of the width of the heating bands which are desired. The depth P of the teeth, and the volume of the spaces between teeth are chosen as a function of the characteristics of the composition which is to be laid down upon the glass in a given length.

The essential part of the apparatus is a toothed roller 10 mounted for free rotation upon a pin 11 in a central vertical slot 12 between the two side portions of a head 13. The head 13 has an upper conduit portion 14 the lower end 15 of which communicates with the central slot 12 in the head and with the then upper portion of the toothed periphery of the roller. The pasty composition to be laid down upon the glass flows downwardly through the orifice 15 into the grooves on the exterior of the roller, such grooves thus being successively filled as the roller rotates past the orifice 15.

It has been found that the deposition in a predetermined quantity of the fluid composition on the surface S of the glass by the roller 10 does not vary substantially with changes of speed of the roller with respect to the glass so long as such speed remains within predetermined known limits. Such an advantageous characteristic results in the transfer of the composition to the spaces between the teeth in the roller, the volume of such spaces being perfectly defined by reason of the outer surface of the lands between the grooves in the roller in intimate contact with the surface of the window 12. This result is particularly interesting since it permits the different bands to be laid down at different or variable speeds or-even with momentary interruptions without any noticeable variation in the transverse section of the bands obtained.

The diameter D of the roller 10 is chosen in such manner as to obtain a convenient length of arc of it toothed peripheral surface in communication with the feeding orifice l5 and a desired length of its engagement with the glass.

The characteristic dimensions of the apparatus may be easily determined by experience and modified as a function of the fluidity of the compositions empl y Thus, for example, resistance bands having a Wid of 0.9 mm. have been easily obtained while employ g an apparatus provided with a toothed wheel or roller 10 made of stainless steel having a width of 0.5 mm., t e

grooves separating the teeth on the roller having a depth P of 0.2 mm., the flanks of the teeth forming an angle A of 45. The head of each tooth has an arcuate length of 0.35 mm., the diameter of the roller being 13 mm. and there being a total of 123 equally spaced teeth on the roller. The toothed roller was moved in contact with the surface S of the glass at a speed of3 meters per minute, the roller being thrust against the glass with a force of about 1 kg., a force sufficient to permit the roller to rotate without slipping on the glass.

The conduit 14 is received within the lower end 16 of a vertical tubular reservoir 17 provided with a stopper 18 at its upper end. A pin 19 prevents the pivoting of the assembly 13, 14 and as a result, the roller 10, with respect to the reservoir 17. The volume of the reservoir is sufficient to provide a satisfactory period of use between charges, thereby to prevent alteration of the composition or of the homogeneity of the composition contained in the reservoir.

The reservoir 17 is mounted in a cylindrical support 20 which has an internal vertical groove 21, the groove slidingly receiving a rib 22 which is integral with the reservoir 17, the rib and groove maintaining the roller in the desired position with respect to the frame 23 of the apparatus. A set screw 24 secures the support 20 to the frame.

Affixed to the lower end of the reservoir 17 is a flange 25, the flange forming a lower seat for a coil compression spring 26, the upper end of the spring engaging the lower end of the support 20. The spring 26 thus thrusts the roller 10 downwardly toward the glass. A threaded collar 27 which is maintained in adjusted position on the threaded upper end of the reservoir 17 by a set screw 28 limits the displacement of the reservoir l7 downwardly and permits the effective compressive force exerted by the spring 26 upon the roller 10 to be adjusted.

The apparatus shown in FIGS. 2-6, inclusive, may be provided with a handle or other suitable means permitting it to be moved manually, in such use of the apparatus there being provided appropriate guiding means (not shown) such templates for causing the roller 10 to travel in the desired path.

As has been indicated above, the total volume of composition dispensed by the apparatus for a given length of band is practically independent of the speed with which the roller 10 moves with respect to the glass. Each groove separating the teeth on the roller is completely filled by the composition upon each of its passages by the orifice of the reservoir 17, and is completely emptied as it passes the surface S of the glass. After being thus deposited upon the glass, the initially substantially separated portions or gobs of composition flow longitudinally and thus join to form a uniform band.

A frame such as that shown at 23 may be provided with one or more apparatuses such as those shown in FIGS. 2-6, inclusive, so as simultaneously to produce a plurality of parallel resistance bands automatically. With apparatus such as that to be described, it is thus possible to obtain, for example, a heated rear window for a vehicle of the type which is shown at 30 in FIG. 7 by depositing simultaneously a plurality of parallel resistance bands 31 upon the glass. This is accomplishcd by mounting a plurality of the apparatuses in the manner of teeth of a comb upon the frame 23, so that all of the apparatuses travel in straight parallel LII lines on the surface of the glass. After the electric resis tance bands have been deposited on the glass, the glass is baked or fired, and bent if necessary.

There may also be made a rear window for a vehicle for the type which is shown at 32 in FIG. 8 wherein there is a plurality of resistance bands 33 in the form of parallel arcs of a circle. In the case of the windows shown in FIG. 7, the frame carrying the different apparatus is displaced in a rectilinear path with respect to the glass; with respect to the window in FIG. 8, on the other hand, the frame is pivoted about the common axis of the concentric resistance bands 33. The paths of the different apparatuses may be neither straight nor circular when the apparatuses are mounted upon the frame so as to be guided in other manners. It is to be noted that the apparatuses which are moved simultaneously travel at different speeds according to the configuration desired (FIG. 8 for example) but, for the reasons indicated above, this does. not result in any inconvenience. In such cases, it is possible to employ rollers 10 of different thicknesses (axial lengths) to obtain bands of different lengths which have the same heating capacities.

Bands such as those shown in 31 and 33 have their extremities connected in parallel by terminal bands, as shown in 34 and 35 respectively. According to another advantageous characteristics of the invention, the resistance bands are perfectly compatible with the formation of the terminal bands 34 and 35, which may be formed ofa similar pasty mixture having a base of silver or an alloy thereof including copper or another metal of high electrical conductivity, said mixture being readily applicable upon the glass by casting or projecting the composition in the form of a liquid.

FIG. 9 shows another form in which a heated rear window 36 of a vehicle may be formed according to the invention. Window 36 has a plurality 37 of resistance bands disposed in parallel upon the glass, such bands having straight segments joined at their ends to parts disposed at angles thereto. The method and the apparatus described above are perfectly satisfactory for making bands of the configuration shown in FIG. 9. FIG. 9 also shows in schematic form an electric circuit for feeding and controlling the resistance bands 37 of the window 36. The terminal bands 38 and 39 are connected at their ends to a source of electric current 40 constituted, for example, by the electric battery of the vehicle. One of the connecting wires, shown at 41, is provided with a switch which is controlled by the operator of the window to be energized or deenergized as desired. The wire 41 and the switch 42 are preferably connected in series with the main switch 43 for all the electrical circuits 45 of the main switch 43 for all the electrical circuits 45 of the vehicle, switch 43 being opcrated by a key 44. A signal, such as the warning light 46, may be connected in the feeding circuit so as to inform the operator as to whether or not the resistance bands are being energized.

One should note the fact that the described apparatus permits a uniform deposition of electrical resistance compositions by adding appropriate substances to the compositions. One may, for example, incorporate in the composition titanium oxide and aluminum oxide in order to increase the electrical resistivity of the composition, or tin oxide in order to lower such resistivity. Such additions naturally produce large variations in the fluidity of the composition but, because of the ability of the apparatus to accommodate compositions of widely varying fluidity, no inconvenience results.

FIG. 1 clearly shows that it is possible to adjust the resistivity of the composition employed throughout a wide range. For a window having known dimensions, one would commence by calculating the total heat energy necessary, taking into account the desired power per unit of surface (for example from 2 to 8 W/dm. (watts per square decimeter) and preferably 4 W/dm.

Taking into account the voltage of the feeding circuit one can easily calculate the total resistance of the resistance bands to be employed. It is thus sufficient to take into consideration the geometric parameters of the heating elements (number, length, and section of the resistance bands) in order to obtain a specific resistivity of the composition to be used and then, by reference to FIG. 1, it is possible to deduce the content of vitreous glaze to be added to the composition.

In operation, the apparatus of FIGS. 2 to 6 has results superior to silk screen methods, it being rather surprising that such indented rollers apply fine lines of uniform section and not as beaded lines. By using appropriate guide means, such as a template, to guide the frame which holds the applicators any number of layers can be superimposed with exact registry, it being understood that baking will be interposed between applications. By thickening parts of the lines with added layers the resistivity of parts of each line can be reduced, concentrating heating effect in the portions not en- Iarged. A gang of applicators may have some wheels wider than others, producing wider lines of less resistance, and concentrating the heating effect in the narrower lines; this can be emphasized by composing some of the lines with greater resistance than others as described in the parent case of which this is a continuation in part. The new apparatus can also be used to apply protective revetments, the frit applicators in the frame being replaced by applicators containing the protective coating material, registry being exactly provided for by the frame and its guide means.

This invention, thus, provides a new and superior method and apparatus, for applying resistance lines to glazings, which is substantially superior to prior methods in commercial use.

By reason of the very large range of compositions which may be employed, in particular in the most interesting part of the curve of FIG. 1 (those compositions having a concentration in vitreous glaze C between 20 and from 50-60% by weight), one may obtain resistance bands of the same width and of equal resistance but having different lengths as a result of their different compositions. Variations of resistivity can be readily obtained by varying the compositions of the bands, which permits all windows in current automobiles to be provided with heating elements in accordance with the invention; such variations are also made by variation in the width of the bands only or by a combination of both. Such variation in resistance may be used advantageously in the case of the systems shown at 33 in FIG. 8, and in system 37 in FIG. 9. The apparatuses utilized for the deposition of such compositions may be fed with compositions having different vitreous glaze contents, as above explained.

The suspension of powdered metal such as silver in vitreous glaze having a low fusion point employed in the compositions according to the invention may be of known classical type. It is thus that the curve of FIG. 1 has been established partially from results obtained with different compositions including a suspension of microscopic flakes of silver in essence of terebenthine, (for example the Preparation dargent F S P l produced commercially by Johnson and Mattews) and a vitreous glaze constituted by a pulverulent frit mixed in a homogeneous fashion with a diluent of oil of the type employed in silk screen printing. For example the powder may be that sold under the trade mark 1-19 I47" and the oil may be that sold under the mark 880 710, both products being produced commercially by Degussa.

As many apparently widely different embodiments of the present invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments.

What is claimed is:

1. Apparatus for simultaneously applying a plurality of parallel strips of electrically conductive resistive material to an insulating sheet, said apparatus comprising a frame and a plurality of applicators, each of said applicators including a cylindrical support adjustably fixable in the frame and a tubular reservoir slideably positioned in the support, the support and reservoir having interengaging means to permit relative axial motion and to prevent relative rotation therebetween, each of said applicators further including a toothed wheel supported in a restricted channel formed at the lower end of the reservoir for rotation about an axis transverse of the length of the reservoir, the angular opening of the teeth of the wheel being substantially 45, resilient means engaged between the support and reservoir urging the reservoir in the direction toward the toothed wheel, and means affixed to the reservoir to limit motion of the reservoir in that direction. 

1. Apparatus for simultaneously applying a plurality of parallel strips of electrically conductive resistive material to an insulating sheet, said apparatus comprising a frame and a plurality of applicators, each of said applicators including a cylindrical support adjustably fixable in the frame and a tubular reservoir slideably positioned in the support, the support and reservoir having interengaging means to permit relative axial motion and to prevent relative rotation therebetween, each of said applicators further including a toothed wheel supported in a restricted channel formed at the lower end of the reservoir for rotation about an axis transverse of the length of the reservoir, the angular opening of the teeth of the wheel being substantially 45*, resilient means engaged between the support and reservoir urging the reservoir in the direction toward the toothed wheel, and means affixed to the reservoir to limit motion of the reservoir in that direction. 